ASPHALTUM AND BITUMINOUS ROCK 399 



The maltha impregnates a clean qualernary iK-u-h s^ind of 

 from 20 to 30 feet in thickness, overlying a bituminoiw shale 

 from which the liquid asphalt exudes. The crude sand con- 

 tahiing about 20 per cent of bitumen is refined lu a product of 

 95 per cent bitumen content. The refined liquid is used to 

 soften solid asphaltum and to coat wood and masonry for pro- 

 tection against the penetration of moisture. 



Asphaltum is found hi beds resultino; from the oxidation 

 either of mmeral tar or, primarily, petroleum. This class in- 

 cludes the immense deposits at Tamauhpas and Moloacan, 

 Mexico. There are many and diversified occurrences of as- 

 phaltum m Europe, the chief deposits being the bituminous 

 limestones at Seyssel, France; at Val de Travers, in Xeuchatel, 

 Switzerland ; in the Dinaric Alps, bordering the eastern coast of 

 the Adriatic sea; and at Ragusa, Italy. In Asia it occurs at 

 many localities in Syria, around the Dead sea, the source of 

 the early supply of asphaltum. 



The largest producmg asphaltum deposit of the world 

 is at Pitch lake, on the island of Trinidad, where the asphal- 

 tum occurs in the form of a basin shaped deposit IS feet thick 

 at the edges and SO feet thick at the middle, with an estimated 

 content of 6,000,000 tons of asphaltum. The deposit is sup- 

 posed to be supported by water, and while solid enough to 

 admit of the passage of wagon and horse, it has a slow move- 

 ment which tends to draw in the tramway used to convey the 

 excavated material to the shore of the lake, unless properl>' 

 supported by branches of trees. In fact, excavations of a 

 depth of 20 feet have become filled m six months. The asphal- 

 tum is broken from the mass by means of picks, before day- 

 light while the material is brittle; it is then loaded on cars and 

 conveyed by the tramway to the shore, from wlience it is car- 

 ried to the pier, 3,500 feet distant, by an aerial wire rope con- 

 veyor and dumped directly into the holds of the vessels. On 

 the voyage it becomes agglomerated into a sohd mass, which 

 must be again broken up by pick in order to remove it from the 

 vessel. The product is roughly refined by heating in tanks and 

 strainmg the liquefied material through a screen for the separ- 

 ation of roots and other vegetable matter with which it is con- 



